Sahany, S., V. Venugopal and R. S. Nanjundiah
Journal of Geophysical Research, Vol. 115, D02103, doi:10.1029/2009JD012644.
Abstract
One of the most important modes of summer season precipitation variability over
the Indian region, the diurnal cycle, is studied using the Tropical Rainfall Measuring
Mission 3-hourly, 0.25°x0.25° 3B42 rainfall product for nine years (1999-2007). Most
previous studies have provided an analysis of a single year or a few years of satellite- or
station-based rainfall data. Our study aims to systematically analyze the statistical
characteristics of the diurnal-scale signature of rainfall over the Indian and surrounding
regions. Using harmonic analysis, we extract the signal corresponding to diurnal and
subdiurnal variability. Subsequently, the 3-hourly time period or the octet of rainfall peak
for this filtered signal, referred to as the "peak octet", is estimated, with care taken to
eliminate spurious peaks arising out of Gibbs oscillations. Our analysis suggests that over
the Bay of Bengal, there are three distinct modes of the peak octet of diurnal rainfall
corresponding to 1130, 1430, and 1730 Indian standard time (IST), from the north central
to south bay. This finding could be seen to be consistent with southward propagation of
the diurnal rainfall pattern reported by earlier studies. Over the Arabian Sea, there is a
spatially coherent pattern in the mode of the peak octet (1430 IST), in a region where it
rains for more than 30% of the time. In the equatorial Indian Ocean, while most of the
western part shows a late night/early morning peak, the eastern part does not show a
spatially coherent pattern in the mode of the peak octet owing to the occurrence of a dual
maxima (early morning and early/late afternoon). The Himalayan foothills were found to
have a mode of peak octet corresponding to 0230 IST, whereas over the Burmese
mountains and the Western Ghats (west coast of India) the rainfall peaks during late
afternoon/early evening (1430-1730 IST). This implies that the phase of the diurnal cycle
over inland orography (e.g., Himalayas) is significantly different from coastal orography
(e.g., Western Ghats). We also find that over the Gangetic plains, the peak octet is around
1430 IST, a few hours earlier compared to the typical early evening maxima over land.
Citation Sahany, S., V. Venugopal and R. S. Nanjundiah, 2010: Diurnal Scale Signatures of Monsoon Rainfall Over the Indian Region from TRMM Satellite Observations. Journal of Geophysical Research, Vol. 115, D02103, doi:10.1029/2009JD012644.